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    SubjectRe: [patch] genapic: optimize & fix APIC mode setup

    * Andi Kleen <ak@suse.de> wrote:

    > On Saturday 11 November 2006 16:14, Ingo Molnar wrote:
    > > From: Ingo Molnar <mingo@elte.hu>
    > >
    > > this patch fixes a couple of inconsistencies/problems i found while
    > > reviewing the x86_64 genapic code (when i was chasing mysterious eth0
    > > timeouts that would only trigger if CPU_HOTPLUG is enabled):
    > >
    > > - AMD systems defaulted to the slower flat-physical mode instead
    > > of the flat-logical mode. The only restriction on AMD systems
    > > is that they should not use clustered APIC mode.
    >
    > This will open a race on CPU hotunplug unfortunately (common for multi
    > core suspend)

    Note that i386 still defaults to logical flat mode, so whatever hotplug
    CPU races there are, they need to be fixed! Given how rare CPU hotplug
    systems are i have no problem with having these races in the kernel for
    a while until it's fixed.

    Also, distro kernels enable CPU_HOTPLUG frequently. It is just ugly
    beyond recognition to switch the programming of the IRQ hardware on
    non-hotplug hardware just because a mostly-software feature (hotplug) is
    enabled ...

    if hotplug breaks suspend then fix it, dont hack it around (on one
    platform) by slowing down the system [and causing other problems] ...

    Ingo
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